1. Field of the Invention
The present invention relates to a communication technique for synchronously transferring data from a single signal source to multi-channel playback devices.
2. Description of the Related Art
A multi-channel speaker system (to be abbreviated as “multi-CH SP system” hereinafter) as the prior art is used together with a digital television, DVD player, AV amplifier, and the like to form a home theater. An interconnection example of a typical home theater has an arrangement shown in FIG. 20. Reference numeral 2001 denotes a digital television (to be abbreviated as “DTV” hereinafter); and 2002, a DVD player (to be abbreviated as “DVD” hereinafter). Reference numeral 2003 denotes an audio video amplifier (to be abbreviated as “AV amplifier” hereinafter); and 2004 to 2009, six speakers (SPs) which form a 5.1CH surround system. For example, reference numeral 2004 denotes a subwoofer (to be abbreviated as “SW” hereinafter); 2005, a center SP; 2006, an L-channel main SP; 2007, an R-channel main SP; 2008, an L-channel rear SP; and 2009, an R-channel rear SP.
As for interconnections among these devices, reference numeral 2030 denotes an interconnection which connects the AV amplifier 2003 and DTV 2001. Typically, the interconnection 2030 comprises a High Definition Multimedia Interface (HDMI) cable used to connect the HDMI output of the AV amplifier 2003 to the HDMI input of the DTV 2001. Reference numeral 2031 denotes an HDMI cable which connects the HDMI output of the DVD 2002 to the HDMI input of the AV amplifier 2003, typically. Reference numerals 2032 to 2037 denote SP cables connected from the AV amplifier 2003 to the six SPs, respectively. On the other hand, as for power supply interconnections, reference numeral 2040 denotes an AC power supply line of the DTV 2001; 2041, a power supply line of the DVD; and 2042, a power supply line of the AV amplifier.
FIG. 20 shows a case in which the SP interconnections are implemented by full-wired interconnections. In this case, the SPs are interconnected by six SP cables from the AV amplifier. These SP cables impose a heavy load on the user since they must be interconnected in consideration of the plus and minus polarities, R and L (right and left) channel differences, and the like. How to simplify many complicated SP interconnections from the AV amplifier is the first issue.
On the other hand, upon actually allocating these SPs, the interconnections to the SPs themselves may often pose a problem such as obstructions to persons' passages in relation to the floor plan of a room.
For example, the interconnections to the R and L surround SPs run across the entrance, and it is not preferable to physically interconnect them.
Upon laying down roundabout interconnections along the wall or ceiling to avoid passage obstructions, the interconnection cable length to each surround SP becomes as long as 5 m or more, thus posing another problem such as deterioration of signal transmission performance, and the like. How to cope with difficulty of physical interconnections to individual SPs is the second issue.
As a method of solving the first issue, a method of connecting a playback audio signal from an optical disk player to playback devices including SPs by, for example, IEEE1394 via a network has been proposed, as described in patent reference 1 (Japanese Patent Laid-Open No. 2001-223588) and patent reference 2 (Japanese Patent Laid-Open No. 2002-217911).
Also, patent reference 3 (Japanese Patent Laid-Open No. 2005-198249), patent reference 4 (Japanese Patent Laid-Open No. 2005-175744), and patent reference 5 (Japanese Patent Laid-Open No. 2005-175745) disclose a surround system by means of a wired bus-connected network system. As an example of the bus-connected network, USB, IEEE1394, and the like are known.
On the other hand, as for the protocol of audio data supplied to such network, non-patent reference (Audio and Music Data Transmission Protocol 2.1 by 1394 TA) is available as public information.
However, these methods pose the following new problems.
(1) Each SP requires a power supply. However, the consumption power of the surround system is around 100 W per CH, and such electric power cannot be supplied via a USB (DC 5 V, 0.5 A) or IEEE1394 (DC 8 to 40 V, 1.5 A) connection cable. For this reason, each SP must individually receive a power supply. Then, the actual interconnection state including power supplies becomes as shown in FIG. 21, resulting in troublesome power supply interconnections. In FIG. 21, reference numerals 2140 to 2145 denote new power supply interconnections to be added.
(2) The cable length is limited to about 5 m, and a relatively expensive cable must be used since it adopts a multi-core structure.
(3) To support the transmission protocol, each device such as the SP or the like must incorporate an advanced-function CPU, resulting in an expensive system.
(4) Due to the audio signal playback requirement for the surround system, playback time management is required. For example, in the case of IEEE1394, such management is achieved using time stamps included in its isochronous data packets. That is, each device holds synchronized clocks, and controls the output timing of playback data based on time stamp information included in incoming received data. Also, hardware for this purpose becomes relatively expensive.
(5) Since IEEE1394 or the like is a standard interface (I/F), if it is used in the surround system, an unexpected device is likely to be connected, and an extra processing function must be provided to cope with errors.
On the other hand, as for the second issue, as a method of solving the problem of these surround SP interconnections, a partial wireless system called a rear-wireless surround system shown in FIG. 22 is available. This system wirelessly connects two, rear-right (R) SP and rear-left (L) SP from the front, and attains wireless interconnections to the SPs allocated farthest from the AV amplifier. In FIG. 22, reference numeral 2201 denotes a wireless transmission adapter; and 2202, a wireless reception adapter. Rear R and L signals are transmitted via a single wireless channel.
However, in practice, as shown examples a to e in FIG. 23, various cases occur depending on installation locations. FIG. 23 shows the example of passage zones assumed depending on allocations in the home, that is, those of ineligible wired interconnection locations. Furthermore, after installation, the room layout may be changed, and failure locations may therefore change. In this way, in the case of devices which are allocated on the living space to provide their functions like the multi-channel SP system, flexibility that allows arbitrarily including wired and wireless connections together becomes an important point. In addition, in the rear-wireless surround system, the total number of interconnections associated with SPs does not always decrease. Hence, the first issue also remains unsolved.